Coal power plant having an associated co2 scrubbing station and heat recovery

ABSTRACT

The invention relates to a method for recovering heat by joining a plurality of heat flows of a fossil-fired, in particular carbon-fired, power plant ( 1 ), which downstream of the combustion comprises a CO 2  scrubbing station ( 58 ) for the flue gas by way of chemical absorption and/or desorption and associated CO 2  compression ( 27 ), which method aims to enable a CO 2  scrubbing station for the flue gas, with associated CO 2  compression, to be integrated into the total energy heat flow and/or the total heat energy balance of a fossil-fired, in particular carbon-fired, preferably conventional, power plant in a way that is advantageous in terms of heating technology. This is achieved by decoupling thermal energy from the heat flow of the CO 2  scrubbing station ( 58 ), with associated CO 2  compression, in the form of at least one partial heat flow (Q 8 , Q 9 , Q 10 , Q 11 ) and coupling it back into a heat flow that is coupled, directly or indirectly, to the heat flow of the boiler ( 2 ) or steam generator of the power plant ( 1 ), and/or by decoupling thermal energy from the flue gas heat flow (Q 3 ) in the form of a partial heat flow (Q 12 , Q 13 , Q 14 ) and coupling it back into the heat flow of the CO 2  scrubbing station ( 58 ) with associated CO 2  compression ( 27 ).

The invention is directed towards a method for heat recovery by connecting a plurality of heat streams of a fossil-fired, in particular coal-fired, power plant having downstream CO₂ scrubbing of the flue gas by way of chemical absorption and/or desorption and associated CO₂ compression. In addition, the invention is directed towards a power plant, in particular a fossil-fired power plant, and preferably a coal-fired power plant, having a CO₂ scrubbing station which is downstream of the combustion and is for the flue gas by means of chemical absorption and/or desorption and associated CO₂ compression.

Since for some time, at the latest since the signing of the Kyoto protocol, intense efforts have been made to reduce the emission into the atmosphere of the gas CO₂ formed in the combustion of fossil fuels, in order to reduce this greenhouse gas in the atmosphere, which greenhouse gas is responsible for climate heating. In the case of fossil-fired, in particular coal-fired power plants, three fundamental process routes are available therefor: separation before combustion, integrated separation, and separation after combustion.

The principle of separation before combustion (pre-combustion) is based on reaction of the fossil fuel to form a synthesis gas consisting of carbon monoxide and hydrogen, wherein, in a further step, the carbon monoxide is oxidized to carbon dioxide (CO₂) and is then removed from the process.

The integrated separation is effected in what is termed the oxy-fuel process. In this case a highly concentrated carbon dioxide (CO₂) exhaust gas stream is generated by combustion of the fossil fuel, in particular coal, with pure oxygen instead of air, which exhaust gas stream, after condensation of the steam fraction, can be directly disposed of without additional scrubbing.

In the third method, separation after combustion (post-combustion), which is used, in particular, in conventional power plants, the carbon dioxide (CO₂) is separated off by a scrubbing station. In this case, the flue gas is largely removed from the flue gas at the end of the flue gas purification line by means of a CO₂ scrubbing station by means of chemical absorption, and so a CO₂-poor exhaust gas leaves the power plant. This CO₂ scrubbing station is located in an absorber, wherein the chemical absorption proceeds using a scrubbing medium, in particular monoethanolamine (MEA), but also diethanolamine (DEA) or methyldiethanolamine (MDEA). The CO₂-loaded scrubbing medium is freed from the CO₂ in a desorber or regenerator and treated and then recirculated to the absorber. A very-high-CO₂-content exhaust gas leaves the desorber or regenerator, which very-high-CO₂-content exhaust gas is liquefied in a subsequent CO₂ compression and thereafter for final storage or reuse is removed from the region of the power plant. The great advantage of this method is that existing conventional power plants can be retrofitted therewith. The disadvantage of this method results from the high energy expenditure necessary for the CO₂ separation. Firstly, a high energy requirement is necessary for regeneration of the scrubbing medium used, which energy requirement is usually covered in the form of steam branched off from the water-steam circuit of the associated power plant. Using this branched-off steam, a reboiler or evaporator of the desorber or regenerator is fed, by means of which the circulated scrubbing medium is heated to the temperature necessary for expelling CO₂. Further energetic expenditure is necessary for subsequent CO₂ compression for liquefaction of the carbon dioxide.

Owing to this relatively high energy expenditure for the CO₂ scrubbing station with associated CO₂ compression, the efficiency of the associated power plant—compared with such a power plant without CO₂ scrubbing—is decreased. Also, the measure of removal of branched-off steam from the water-steam circuit of the power plant has an effect on this circuit and the energy streams, in particular the heat energy streams of the power plant.

The object of the invention is to provide a solution which makes possible a thermally favorable integration of a CO₂ scrubbing of the flue gas with associated CO₂ compression into the overall heat stream and/or the overall thermal energy balance of a fossil-fired, in particular coal-fired, preferably conventional, power plant.

In a method of the type described in more detail at the outset, this object is achieved in that, from the heat stream of the CO₂ scrubbing station with associated-CO₂ compression, thermal energy in the form of at least one heat substream is extracted and fed back into a heat stream that is coupled directly or indirectly to the heat stream of the boiler or steam generator of the power plant and/or in that, from the flue gas heat stream, thermal energy in the form of at least one heat substream is extracted and fed back into the heat stream of the CO₂ scrubbing station with associated CO₂ compression.

In a development of the invention this can be implemented in that thermal energy available in the region of the CO₂ scrubbing station with associated CO₂ compression is decoupled or extracted from the heat stream of the CO₂ scrubbing station with associated CO₂ compression as a heat substream by means of at least one plant component that is utilizable there as a heat source, and/or thermal energy available in the region of a flue gas line is decoupled or extracted from the heat stream of the flue gas by means of at least one plant component that is utilizable there as a heat source and the thermal energy in the region of the power plant obtained respectively by the decoupling or extraction in the form of the at least one heat substream is fed back into the heat stream of the power plant outside the respective decoupling or extraction region by means of at least one further plant component that is utilizable there in each case as heat sink for the thermal energy obtained.

Likewise, the abovementioned object is achieved in a power plant of the type described in more detail at the outset in that, in the region of the CO₂ scrubbing station with associated CO₂ compression, at least one plant component that is utilized as heat source and effects the decoupling or extraction of thermal energy from the heat stream of the CO₂ scrubbing station with associated CO₂ compression is arranged and/or constructed, and/or, in the region of a flue gas line and/or a bypass flue gas line bypassing an air preheater, at least one plant component that is utilized as heat source and effects the decoupling or extraction of thermal energy from the flue gas stream is arranged and/or constructed, and in the region of the power plant, at least one, preferably a further, plant component which is connected in a heat-energy-conducting manner to the first plant component and is used as a heat sink and effects the feeding back of the decoupled or extracted thermal energy into the heat stream of the power plant outside the respective decoupling or extraction region is arranged and/or constructed.

In this case the method is further distinguished in that thermal energy available in a CO₂-rich gas stream and/or in the absorption medium used is decoupled or extracted in the region of the CO₂ scrubbing station with associated CO₂ compression.

In addition, the invention, in an embodiment of the method, provides that thermal energy available in the flue gas is decoupled or extracted in the region of the flue gas line and/or in the region of a bypass flue gas line bypassing an air preheater.

In the case of an energy extraction in the region of the CO₂ scrubbing station with associated CO₂ compression, it is in addition advantageous if the thermal energy that is decoupled or extracted in the region of the CO₂ scrubbing station with associated CO₂ compression is fed back into the heat stream of the power plant outside the region of the CO₂ scrubbing station with associated CO₂ compression, in particular into the water-steam circuit and/or a district heating circuit and/or into a coal-bearing coal line and/or a fresh air line, in particular having associated flue gas bypass line, in particular air preheater bypass, for feeding heat into WT14, WT17 and/or WT13.

In the case of heat extraction in the region of the flue gas line and/or the bypass flue gas line, it is in addition expedient if the thermal energy which is decoupled or extracted in the region of the flue gas line and/or in the region of the bypass flue gas line is fed back outside the region of the flue gas line and/or the bypass flue gas line into the water-steam circuit and/or the district heating circuit and/or the region of the CO₂ scrubbing station with associated CO₂ compression, in particular into a heat exchanger of a reboiler.

Expedient embodiments and advantageous developments not only of the method according to the invention but also the power plant according to the invention are subject matter of the respective (further) subclaims.

As a result of the invention, the CO₂ scrubbing station of the flue gas by means of chemical absorption and/or desorption and associated CO₂ compression is and/or can be integrated thermally expediently and in an optimized manner into the overall heat stream and thereby the overall thermal energy balance of a fossil-fired, in particular coal-fired, preferably conventional, power plant.

Firstly, it is proposed that waste heat streams formed in the region of the CO₂ scrubbing station and in the region of the CO₂ compression are used as heat source(s). In this case, a heat source is taken to mean the possibility of decoupling and extracting unrequired thermal energy in the form of at least one heat substream from the respective waste heat stream, that is to say a medium carrying thermal energy in the form of measurable heat, and thereafter feeding it in a heat-energy-conducting manner to a heat sink arranged at another point of the power plant outside the region of the CO₂ scrubbing of the flue gas with associated CO₂ compression. A heat sink in this case is taken to mean that the thermal energy that is fed in a heat-conducting manner and is extracted or decoupled in the region of the CO₂ scrubbing station with associated CO₂ compression is fed back into the heat stream of the power plant, i.e. it is transferred to a medium of a lower thermal energy level, i.e. a lower temperature, that is running or flowing there, and thereby heat taken off from the region of the CO₂ scrubbing station with associated CO₂ compression is recirculated and recovered. The thermal energy which otherwise leaves unutilized the region of the CO₂ scrubbing station of the flue gas with associated CO₂ compression together with the purified flue gas stream or with the liquefied carbon dioxide stream is according to the invention therefore at least in part utilized and recirculated to the heat stream of the power plant in the course of heat recovery.

Secondly, for improving and optimizing the overall heat stream and the overall thermal energy balance of the power plant, it is provided that on the flue gas side in the direction of flue gas flow upstream of the CO₂ scrubbing station, thermal energy in the form of a heat substream is decoupled or extracted from the thermal energy present in the flue gas and in the region of the CO₂ scrubbing station, in particular in the region of the reboiler or evaporator there, is fed back into the heat stream of the CO₂ scrubbing station. This embodiment may also be implemented independently of the above-described decoupling and extraction of thermal energy from the region of the CO₂ scrubbing station with associated CO₂ compression.

Further possibilities for the use and feeding back into the overall heat stream of the power plant of thermal energy which is decoupled or extracted from the flue gas in the region of the flue gas line or a bypass flue gas line bypassing the air preheater are according to the invention feeding the decoupled or extracted thermal energy back into the water-steam circuit of the power plant, and here preferably in the region of the low-pressure preheater and/or the high-pressure preheater, and/or into an associated district heating circuit. This use or recoupling of thermal energy that is decoupled or extracted on the flue gas side is preferably provided in combination with thermal energy that is decoupled or extracted from the region of the CO₂ scrubbing station with associated CO₂ compression and fed back into the heat stream of the power plant in the region outside the CO₂ scrubbing station with associated CO₂ compression. In particular, in this context, it is expedient if the fresh air fed to the boiler or steam generator of the power plant is then heated by way of a heat exchanger to which thermal energy which is decoupled or extracted from the region of the CO₂ scrubbing station with associated CO₂ compression is fed for delivery to the inflowing fresh air mass stream.

In supplementation, in a manner which is not shown, it can additionally be provided that solar-heating or geo-thermal energy production systems are assigned to the power plant, the energy thereof that is produced therein being fed or made available to the heat stream of the power plant in the form of thermal energy.

It is particularly advantageous if the decoupling or extraction at the CO₂ scrubbing station desorber or regenerator top proceeds downstream of the CO₂ compression and in the direction of flow of CO₂. Advantageous sites for the construction of heat sources or heat sinks for the decoupling or extraction of thermal energy are, in addition, in the region of the CO₂ scrubbing station absorber intercooler and in the region of the CO₂ compression intercooler. Particularly advantageous sites for feeding back in the extracted thermal energy are the region of the low-pressure pre-heater and also the region in the direction of flow downstream of a condensate pump arranged downstream of a condenser, wherein the above regions are all constructed in the water-steam circuit of the power plant. Further advantageous sites for the construction of heat sources or heat sinks for feeding back in the thermal energy which is extracted in the region of the CO₂ scrubbing station with associated CO₂ compression are the district heating circuit assigned to the power plant, the fresh air heating of the fresh air that is to be supplied to the burners of the power plant or the coal drying station of the coal that is to be supplied to a coal mill as fossil fuel. This applies in particular in the use of brown coal, wherein the method according to the invention and the power plant according to the invention, however, are applicable not only in the case of hard coal firing but also brown coal firing.

The method according to the invention is further distinguished in that the thermal energy is decoupled or extracted by means of one or more heat sources formed at the CO₂ scrubbing station desorber or regenerator top and/or downstream of the CO₂ compression in the CO₂ flow direction and/or in the region of the CO₂ scrubbing station absorber intercooler and/or in the region of the CO₂ compression intercooler, and the thermal energy is fed back in by means of one or more heat sinks formed in the region of the low-pressure preheater and/or in the condensate flow direction upstream of the low-pressure preheater and/or in a district heating circuit and/or in a fresh air heater and/or in a coal drying station and heat-energy-conductingly connected to the heat source(s).

A further advantageous embodiment of the invention is that the thermal energy is decoupled or extracted by means of one or more heat sources formed in the flue gas line and/or in the bypass flue gas line and the thermal energy is fed back into the water-steam circuit in the region of the low-pressure preheater and/or the high-pressure preheater and/or into the district heating circuit and/or into the region of the CO₂ scrubbing station, in particular into the reboiler, preferably a heat exchanger of the reboiler.

It is likewise advantageous when the thermal energy which is decoupled or extracted in the region of the CO₂ scrubbing station with associated CO₂ compression is fed back into the heat stream of the power plant by means of heat exchangers arranged in a Rankine cycle.

For carrying out the method, it is particularly expedient according to the invention if the method is carried out in a power plant as claimed in any one of claims 11 to 29.

Likewise, the power plant, in an embodiment of the invention, is therefore distinguished in that one or more plant components utilized as heat source(s) for heat transfer is/are arranged and/or formed at the CO₂ scrubbing station desorber or regenerator top and/or downstream of the CO₂ compression in the CO₂ flow direction and/or in the region of the CO₂ scrubbing station absorber intercooler and/or in the region of the CO₂ compression intercooler, each of which plant components is heat-energy-conductingly connected in a manner bearing a heat-carrier medium to one or more plant components arranged in the region of the low-pressure preheater and/or in the condensate flow direction upstream of the low-pressure preheater and/or in a district heating circuit and/or in the fresh air heater and/or in the coal drying station and, as heat sink(s), effecting a heat transfer.

A possibility that may be readily implemented in terms of the method and the plant of forming heat sources and heat sinks is to use plant components that are present therefor and/or are formed as additional heat exchangers. The invention, therefore, in a further embodiment also provides with respect to the power plant that at least one plant component, preferably a heat exchanger, forming a heat source, in particular for a separate heat-carrier medium, is formed in the region of the CO₂ scrubbing station with associated CO₂ compression and is connected in the manner heat-energy-conductingly bearing a medium, preferably the separate heat-carrier medium, to at least one further plant component arranged in the region of the power plant, preferably a further heat exchanger, forming a heat sink, in particular for the separate heat-carrier medium, wherein one or more of the plant components selected from a heat exchanger at the CO₂ scrubbing station desorber or regenerator top and/or a heat exchanger downstream of the CO₂ compression and/or a heat exchanger of the CO₂ scrubbing station absorber intercooler and/or a heat exchanger of the CO₂ compression intercooler each form a heat exchanger acting as a heat source, and/or a line conducting high-CO₂-content gas downstream of a desorber forms a plant component utilized as a heat source, and/or a line conducting liquid CO₂ downstream of the CO₂ compression forms a plant component utilized as a heat source, and also one or more of the plant components selected from a heat exchanger of the low-pressure preheater and/or a heat exchanger upstream of the low-pressure preheater and/or a heat exchanger in the district heating circuit and/or a heat exchanger of the coal drying station and/or a heat exchanger of the fresh air heater each form a further heat exchanger acting as heat sink.

One possibility of implementing the decoupling of thermal energy and feeding of thermal energy back in is, in particular, that the heat exchanger forming a heat source at the CO₂ scrubbing station desorber or regenerator top is heat-energy-conductingly connected to a heat exchanger, forming a heat sink, of the low-pressure preheater, in particular to the heat exchanger next to a condensate pump positioned on the upstream side to the condensate flow direction.

A further possibility for advantageously implementing the extraction of thermal energy and feeding it back in is, in addition, that the heat exchanger forming a heat source is heat-energy-conductingly connected downstream of the CO₂ compression to a heat exchanger, forming a heat sink, of the low-pressure preheater, in particular to the heat exchanger next to a feed water vessel in the condensate flow direction, and/or to the heat exchanger, forming a heat sink, upstream of the low-pressure preheater.

In this case, it is then particularly expedient when the heat exchanger, upstream of the low-pressure preheater, is arranged in a condensate line downstream in the condensate flow direction of a condensate pump, and/or the heat exchangers of the low-pressure preheater are arranged in a bypass line branching off from the condensate line, which the invention likewise provides.

According to a further embodiment, a thermally particularly expedient coupling together of the heat exchangers WT2 and WT5 may be achieved in that the return of the heat exchanger of the low-pressure pre-heater is heat-energy-conductingly connected to the flow of the heat exchanger upstream of the low-pressure preheater.

A further advantageous and expedient heat-energy-conducting connection between the individual heat sources and the individual heat sinks may be achieved, in particular, if, between the heat sources and the heat sinks, a heat-carrier medium, in particular a heat-carrier medium separate from the remaining mass flow of the power plant, is circulated between them, which is preferably the case when the heat sources and heat sinks are formed as heat exchangers. The invention, in a further embodiment, therefore also provides that a heat-carrier medium is conducted in a circuit formed by the heat exchanger downstream of the CO₂ compression, the heat exchanger next to a feed water vessel in the condensate flow direction and the heat exchanger upstream of the low-pressure preheater and/or is conducted in a circuit formed by the heat exchanger at the CO₂ scrubbing station desorber or regenerator top and the heat exchanger next to a condensate pump positioned in the upstream-side condensate flow direction, in each case through these heat exchangers.

An expedient possibility for forming heat recovery also comprises feeding the decoupled or extracted thermal energy back into the district heating circuit of a power plant, if such a district heating circuit is provided. Therefore, in an embodiment, the invention also provides that the heat exchanger at the CO₂ scrubbing station desorber or regenerator top and/or the heat exchanger downstream of the CO₂ compression is/are heat-energy-conductingly connected to one or more heat exchangers arranged in the district heating circuit.

In this case, a pipe connection and coupling between the heat exchangers arranged in the district heating circuit and the heat exchangers arranged in the region of the water-steam circuit of the power plant can be advantageous, for which reason the invention is also distinguished in that one or more of the heat exchangers arranged in the district heating circuit is/are heat-energy-conductingly connected to one or more of the heat exchangers associated with or arranged upstream of the low-pressure preheater.

In this case, again, the heat exchanger can be arranged upstream of the low-pressure preheater in the return of the heat exchanger arranged in the district heating circuit and/or in the return of the heat exchanger associated with the low-pressure preheater.

Owing to the possibility, by extracting thermal energy in the region of the CO₂ scrubbing station with associated CO₂ compression, of providing a sufficiently high amount of heat energy or sufficiently high amount of thermal energy for feeding it back in, there is a further embodiment according to the invention of the power plant in that the heat energy supply for the reboiler or evaporator is constructed to be integrated into the district heating circuit (the expressions “heat energy” and “thermal energy” are used as synonyms in the present text).

A further possibility for using the thermal energy recovered by extraction is to use it for coal drying and/or for fresh air heating. An advantageous use according to the invention therefore comprises in addition that the heat exchanger at the CO₂ scrubbing station desorber or regenerator top and/or the heat exchanger downstream of the CO₂ compression is/are heat-energy-conductingly connected to one or more heat exchangers arranged in a power plant coal line connected to a coal mill.

Likewise, the invention also provides that the heat exchanger at the CO₂ scrubbing station desorber or regenerator top and/or the heat exchanger downstream of the CO₂ compression is/are heat-energy-conductingly connected to one or more heat exchangers arranged in a fresh air line feeding fresh air to the boiler of the power plant.

In an advantageous embodiment the invention further provides that the at least one heat exchanger arranged in the bypass flue gas line is heat-energy-conductingly connected to the water-steam circuit of the power plant in the region of the low-pressure preheater or the high-pressure preheater.

In a further development, it is, furthermore, provided that a heat exchanger arranged in the bypass flue gas line is heat-energy-conductingly connected to the district heating circuit.

According to a development of the invention, it is furthermore advantageous that a heat exchanger arranged in the bypass flue gas line is heat-energy-conductingly connected to the reboiler and/or to a heat exchanger of the reboiler.

It is then, in addition, advantageous when a heat exchanger heat-conductingly connected to the district heating circuit and/or a heat exchanger heat-conductingly connected to the water-steam circuit of the power plant, preferably in the region of the low-pressure preheater, is arranged in the reboiler return.

Finally, the invention also provides that the heat exchanger at the CO₂ scrubbing station desorber or regenerator top and/or the heat exchanger downstream of the CO₂ compression and/or the heat exchanger of the CO₂ scrubbing station absorber intercooler and/or the heat exchanger of the CO₂ compression intercooler is/are heat-conductingly connected to a heat exchanger arranged in a Rankine cycle.

Of course, the abovementioned features and the features still to be described hereinafter are usable not only in the combination stated in each case, but also in other combinations. The scope of the invention is only defined by the claims.

The invention is described in more detail by way of example hereinafter with reference to a drawing. In the drawing

FIG. 1 shows, schematically, power plant components of a coal-fired, in particular brown-coal-fired, power plant,

FIG. 2 shows, schematically, power plant components of a coal-fired power plant having heat (re-) feeding of thermal energy extracted in the region of the CO₂ scrubbing station having associated CO₂ compression into the water-steam circuit and into a district heating circuit associated with the power plant,

FIG. 3 shows, schematically, the district heating circuit according to FIG. 2 having additionally integrated evaporator heating,

FIG. 4 shows, schematically, an alternative embodiment of a heat (re-)feeding into a district heating circuit,

FIG. 5 shows, schematically, a heat (re-)feeding into a coal conveyor and/or coal dryer of a coal mill associated with a power plant,

FIG. 6 shows, schematically, a heat (re-)feeding into the fresh air heating of a fresh air line feeding fresh air to burners of a boiler of the power plant,

FIG. 7 shows, schematically, a heat (re-)feeding of thermal energy extracted in the region of the CO₂ scrubbing station with associated CO₂ compression and of thermal energy extracted in the region of a bypass flue gas line into the water-steam circuit of the power plant,

FIG. 8 shows, schematically, a heat (re-)feeding corresponding to FIG. 7 with additional heat (re-)feeding into an associated district heating circuit,

FIG. 9 shows, schematically, an indirect steam heater of a water circuit of an indirect heating system of a reboiler,

FIG. 10 shows, schematically, heat (re-)feeding into a Rankine cycle,

FIG. 11 shows, schematically, extraction of thermal energy in the region of a bypass flue gas line and feeding of the thermal energy in the region of the evaporator/reboiler of the desorber of the CO₂ scrubbing station,

FIG. 12 shows, schematically, a heat (re-)feeding according to FIG. 11 supplemented by a fresh air preheater and

FIG. 13 shows, schematically, an outline diagram of various heat substreams of a power plant having a plurality of heat substreams connecting heat streams of the power plant for heat recovery.

FIG. 13, schematically, shows an outline diagram of a power plant overall designated 1, the steam generator or boiler 2, a turbine set 76, preferably comprising high-pressure turbines 3, medium-pressure turbines 4 and low-pressure turbines 5, a CO₂ separator 77 comprising a CO₂ scrubbing station 58 with associated CO₂ compression 27, and an associated district heating grid 78 comprising a district heating circuit 44. These plant components 2, 76, 77 and 78 are mutually connected to one another via various heat substreams, wherein these heat substreams together form the total heat stream and the total thermal energy balance of the power plant 1. Of these heat substreams, in FIG. 13, the water-steam circuit is designated Q₁, the district heating integration Q₂, the flue-gas-side heat stream connection of the CO₂ separator 77 to the boiler 2 as Q₃, the heat stream fed with the air to the boiler as Q₄, the heat stream fed by way of the coal to the boiler 2 as Q₅, the low-CO₂ waste gas heat stream leaving the CO₂ separator as Q₆ and the heat substream leaving the CO₂ separator 77 of the high-CO₂-content medium as Q₇, wherein all substreams Q₁ to Q₇ are shown with dashed lines. According to the invention, then, heat substreams Q₈ to Q₁₁ are branched off and decoupled from the heat stream forming within the CO₂ separator 77, as indicated by the correspondingly labeled arrows shown in continuous lines, and recirculated to other heat substreams and thereby the total heat stream of the power plant 1. Likewise, from the flue-gas-side heat substream Q₃, the heat substreams Q₁₂ to Q₁₄ are branched off or decoupled and, corresponding to the arrow drawing, likewise fed (back) into the total heat stream of the power plant 1. In this case, the heat substream Q₈ is extracted from the CO₂ separator 77 and fed into the heat substream Q₁ conducted in the water-steam circuit of the power plant 1. The heat substream Q₉ is extracted from the CO₂ separator 77 and fed into the district heating circuit 44 of the district heating grid 78 and thereby, in principle, to the heat substream Q₂. The heat substream Q₁₀ is extracted or decoupled from the CO₂ separator 77 and fed to the heat substream Q₄ of the fresh air feed and fed (back) into this. The heat substream Q₁₁ is likewise extracted from the heat stream of the CO₂ separator 77 and then fed (back) into the heat substream Q₅ conducted in a coal line 55 leading to a coal mill 54 and/or the boiler 2. Likewise, a heat substream Q₁₂ is extracted from the flue-gas-side heat substream Q₃, which heat substream Q₁₂ is fed (back) into the heat substream conducted in the CO₂ separator 77. In addition, from the heat substream Q₃, the heat substreams Q₁₃ and Q₁₄ are extracted, of which the heat substream Q₁₃ is fed back into the heat substream Q₁ of the water-steam circuit of the power plant 1 and the heat substream Q₁₄ is fed back into the district heating circuit 44 of the district heating grid 78.

The power plant designated in FIG. 1 overall with 1 is shown schematically in the upper partial picture with the water-steam circuit thereof connected to the boiler 2 and in the lower partial picture with the flue gas path thereof connected on the flue gas side to the boiler 2 with the flue gas CO₂ scrubbing by way of chemical absorption and associated CO₂ compression 27 downstream of the combustion proceeding in the boiler 2. On the water-steam circuit side, the power plant comprises a high-pressure turbine 3, two medium-pressure turbines 4 and four low-pressure turbines 5, wherein the number of turbines is merely by way of example. At the end of the turbine section, a generator is arranged. Downstream of the last low-pressure turbine 5, in the water-steam circuit a condenser 7 is arranged which as usual is connected to a cooling tower 8. In the direction of flow of the condensate, a condensate pump 9 is arranged downstream of the condenser 7 in the water-steam circuit, which condensate pump 9 feeds the condensate to a low-pressure preheater 10 comprising five heat exchangers. The low-pressure preheater 10 is connected to a feed water vessel 11 with associated feed water pump 12 which feeds the feed water originating from the feed water vessel 11 to a high-pressure preheater 13, whereafter it then passes into the steam generator of the boiler 2. In addition, steam lines departing from the respective turbines 3, 4, 5 are drawn in the water-steam circuit. To this extent, this part of the power plant comprises components as are known from conventional coal-fired power plants. In addition, the water-steam circuit of the power plant 1 has, furthermore, three heat exchangers WT1, WT2 and WT5. The heat exchanger WT5 thereof is integrated into the condensate line 14 leading to the feed water vessel 11 upstream of the low-pressure preheater, more precisely in the direction of flow of the condensate, downstream of the condensate pump 9, but upstream of the low-pressure preheater 10. The heat exchangers WT1 and WT2 are arranged in a bypass line 15 branching off from the condensate line 14, in the direction of flow of the condensate downstream of the heat exchanger WT5, and opening out back into the condensate line 14 downstream of the low-pressure preheater 10, but upstream of the feed water vessel.

The boiler 2 is fired, as indicated by the arrow 16, with air and coal. The flue gas leaving the boiler 2 via the flue gas line 17 is fed to a flue gas treatment 18 at least comprising the components denitration system, electrostatic precipitator and flue gas desulfurization system, and then passes into a decarbonization system 19 comprising a CO₂ scrubbing station 58 with associated CO₂ compression 27.

In this decarbonization system 19 connected downstream of the combustion, the CO₂ present in the flue gas is removed by way of chemical absorption using a scrubbing medium. The scrubbing medium used is preferably MEA (monoethanolamine, H₂N—CH₂—CH₂—OH) or else DEA (diethanolamine, HO—CH₂—CH₂—NH—CH₂—CH₂—OH) or MDEA (methyldiethanolamine, HO—CH₂—CH₂—NCH₃—CH₂—CH₂—OH). In this case the actual scrubbing of the flue gas or exhaust gas by way of the scrubbing medium takes place in an absorber 20 or an absorption column through which the flue gas flows in countercurrent to the scrubbing medium. The flue gas leaves the absorber 20 at the top end thereof as a low-CO₂ exhaust gas 21. In order to reprocess the scrubbing medium or solvent loaded in the absorber 20 and regenerate it for long-term use, desorber or regenerator 22, preferably in the form of a desorption column, is connected downstream of the absorber 20, to which desorber or regenerator the CO₂-rich scrubbing medium or solvent is fed after it flows through the absorber 20. For regenerating the scrubbing medium and expelling the CO₂ from the scrubbing medium, a high energy requirement is necessary which is fed to the evaporator or the reboiler 23 of the desorber/regenerator 22 in the form of steam tapped off from the water-steam circuit, as is indicated in the upper partial picture of FIG. 1 by the dashed line and the letters D₁ in this region and also at the reboiler 23. The return S1 of the heat exchanger 24 arranged in or on the evaporator 23 opens out into the condensate line of the water-steam circuit downstream, in the direction of flow of the condensate, of the low-pressure preheater 10 and upstream of the feed water vessel 11.

Before entry into the absorber 20, the flue gas which is at first unpressurized is isothermally compressed to a pressure of below 10 bar, for example 2 bar, and then conducted through the absorber 20, wherein the scrubbing medium or solvent flows countercurrently thereto. The CO₂-rich scrubbing medium or solvent is thereafter, with flow through a heat exchanger 25, introduced into the desorber/regenerator 22. In the desorber/regenerator 22, the CO₂-rich scrubbing medium is broken up and regenerated by heating, and so at the top end of the desorber/regenerator 22 a virtually pure CO₂—H₂O mixture exits which can be separated by a condensation process, and so then an approximately 90% pure CO₂ stream is released which is fed via a line 26 to a CO₂ compression system, which is ten-stage in the working example, to the CO₂ compression 27, which compresses the CO₂ stream to approximately 100 bar and liquefies it. Thereafter the liquefied CO₂ is fed by way of a line 28 to further use or storage.

Since high temperatures are necessary for the desorption/regeneration of the scrubbing medium in the desorber/regenerator 22, the CO₂-rich scrubbing medium stream or solvent stream in the heat exchanger 25 is heated to approximately 95° C. This is achieved using low-CO₂ scrubbing medium or cleaning agent 29 which is likewise passed through the heat exchanger 25 and regenerated in the desorber/regenerator 22 and sufficiently heated/cooled in the evaporator/reboiler 23. The evaporator or reboiler 23 vaporizes a part of the solvent, as a result of which the carbon dioxide is desorbed from the scrubbing medium or solvent, in such a manner that at the top end a virtually pure CO₂—H₂O mixture forms which passes into the condenser 31 at the top of the desorber/regenerator 22 where the water condenses out, in such a manner that a virtually pure CO₂ stream is withdrawn. The regenerated low-CO₂ scrubbing medium or solvent 29 is taken off at the bottom of the desorber/regenerator 22, conducted via the heat exchanger 25 in which the countercurrently flowing, loaded, CO₂-rich scrubbing medium stream or solvent stream 30 is heated. After passage through a pump, brought to the necessary absorber pressure and correspondingly cooled, the low-CO₂ scrubbing medium or solvent 29 is fed back to the absorber 20. Since, during the entire process, losses of water and scrubbing medium result, these are added to the system again at a mixing point 32.

A plant component is arranged in line 26 on the CO₂ scrubbing station desorber top or regenerator top of the desorber/regenerator 22, which plant component is used as a heat source in the form of a heat exchanger 33. In the direction of flow of the CO₂—H₂O-rich gas stream, downstream of the heat exchanger 33, in addition, a condensate collection vessel 34 is arranged in the line 26, using which, owing to the cooling of the CO₂—H₂O stream conducted in line 26, as a consequence of the heat exchanger 33, H₂O which condenses out can be collected. A further heat exchanger 35 likewise forming a plant component which is used as a heat source, serving for cooling the liquefied CO₂ stream is arranged in line 28 downstream of the CO₂ compression station 27. Further plant components utilized as heat sources in the form of heat exchangers 36 are provided as heat exchangers of the CO₂ scrubbing station absorber intercooler, wherein a heat exchanger 36 arranged at the top of the absorber 20 is also considered to belong to the CO₂ scrubbing station absorber intercooler. In total, in the working example, four heat exchangers 36 are present. In addition, plant components used as heat sources are also arranged between the compressors 38 of the CO₂ compression station 27 in the form of heat exchangers 37 of the CO₂ compression intercooler. In the working example, six heat exchangers 37 are shown between the compressors 38, but in the case of the ten compressors 38 that are present, up to nine heat exchangers 37 of the CO₂ compression intercooler can be present. Since all these heat exchangers 33, 35, 36 and 37 serve for cooling, at the same time they form a heat source for the heat-carrier medium still otherwise conducted in each case in the heat exchangers 33, 35 to 37. This function of the heat exchangers 33, 35 to 37 as heat source is then utilized according to the invention for recovering a part of the energy taken off via the tapped-off steam line D1 from the water-steam circuit of the power plant 1 and to feed it back to the power plant 1, in particular to the water-steam circuit or other regions or plant parts which are connected to the power plant 1. For this purpose there serve heat exchangers WT1-WT11 positioned at the corresponding points which, as will be explained hereinafter, each form a plant component utilized as a heat sink, using which in each case thermal energy may be transferred to a heat substream. Using the heat exchangers 33, 35 to 37 acting as a heat source for a heat-carrier medium conducted therein, in the region of the CO₂ scrubbing station and of the decarbonization system 19 comprising the associated CO₂ compression 27, thermal energy is decoupled from the heat stream of the decarbonization system 19, transferred to the heat-carrier medium flowing in the heat exchangers 33, 35 to 37 and thereafter, by release from this heat-carrier medium using the heat exchangers WT1-WT11 forming heat sinks for the heat-carrier medium, is fed back as thermal energy into the heat stream of the power plant system at another point.

In the working example according to FIG. 1, decoupling or extraction of thermal energy proceeds from the heat stream of the CO₂ scrubbing station 58 with associated regenerator 22 and associated CO₂ compression 27 by means of the heat exchangers 33 and 35.

In the working example according to FIG. 1, the heat exchanger 33 acting as a heat source is connected in the flow via the line 39 and in the return via the line 40 to the heat exchanger WT1 of the low-pressure preheater that is arranged in the bypass line 15 acting and used as heat sink. In the lines 39, 40, a heat-carrier medium circulates which takes up thermal energy in the heat exchanger 33 and releases it in the heat exchanger WT1 to the condensate flowing in the bypass line 15 and thus feeds it back into the actual heat stream of the power plant 1. Likewise, the heat exchanger 35 acting as a heat source is connected via a line 41 to the heat exchanger WT2 arranged in the bypass line 15 that is acting and utilized as a heat sink. The return of the heat exchanger WT2 of the low-pressure preheater is connected via a line 42 to the heat exchanger WT5 arranged in the condensate line 14 and likewise forming a heat sink. On the return side, the return of the heat exchanger WT5 is connected via a line 43 again to the heat exchanger 35. Here also, a heat-carrier medium circulates in the lines 41, 42 and 43. Here, accordingly, thermal energy is decoupled from the heat stream of the CO₂ scrubbing station 58 with associated desorber 22 and associated CO₂ compression 27 and fed back into the actual heat stream of the power plant 1 at two points, namely the plant components in the form of the heat exchangers WT2 and WT5 used as heat sinks. In an embodiment which is not shown, it is also possible to dispense with the heat exchangers 33 and 35 and instead to connect the line 26 to the heat exchanger WT1 and the line 28 to the heat exchangers WT2 and WT5, and so the CO₂-rich gas transported in the line 26 and also the liquid CO₂ transported or conveyed in line 28 functions directly as heat-carrier medium, from which thermal energy is decoupled and fed back into the water-steam circuit via the heat exchangers WT1, WT2 and WT5. In this case, then, in the region of the CO₂ scrubbing station with associated CO₂ compression, and in the region of the power plant, in each case one plant component, in the present example the heat exchangers 35 and WT2 combined to form one unit and the heat exchangers 33 and WT1 combined to form one unit are present, which in the region of the CO₂ scrubbing station with associated CO₂ compression are both used as heat source and effect the decoupling or extraction of thermal energy and are used as heat sink in the region of the power plant 1 and effect the feeding back of the thermal energy extracted or decoupled in the region of the CO₂ scrubbing station with associated CO₂ compression.

In the working example, however, in each case one circuit of a separate heat-carrier medium, as indicated by lines 39, 40 and 41 to 43, is provided, in which water circulates as a separate heat-carrier medium.

In the region of the heat exchanger 35, the liquid CO₂ stream transported in the line 28 is at a temperature of approximately 185° C., wherein the heat exchanger 35 serves as heat source for the heat-carrier medium conveyed in the lines 41, 42 and 43 which gives off the thermal energy taken up to the cool condensate at approximately 18° C. downstream of the condensate pump 9 in the direction of flow of the condensate, which, in an amount of approximately 2/3 of the entire condensate stream conducted through the condensate line 14, passes by the low-pressure preheater 10 via the bypass line 15 and is warmed using the heat exchanger WT2 acting as a heat sink, in such a manner that the condensate before returning into the line 14 or the feed water vessel 11 has a temperature of approximately 120° C. The return of the heat exchanger WT2 leading to the heat exchanger WT5 then still has a temperature high enough that the heat exchanger WT5 likewise can, and according to the working example also is, used as a heat source for the heat retransfer into the condensate flowing in the line 14, wherein the heat exchanger WT5 in the context of the invention, however, forms a heat sink for the thermal energy obtained in the region of the CO₂ scrubbing station.

In addition to the plant components forming a heat source for the decoupling or extraction of thermal energy from the heat stream of the CO₂ scrubbing station with associated CO₂ compression 27, heat exchanger 33 on the CO₂ scrubbing station desorber top or regenerator top and heat exchanger 35 downstream of the CO₂ compression 27, a further heat exchanger 24 is provided on the reboiler or evaporator 23 of the desorber/regenerator 22. This heat exchanger 24, however, forms a heat sink, in the meaning of the terminology used here, using which thermal energy is fed back into the heat stream of the CO₂ scrubbing station with associated CO₂ compression. Here, tapped steam D1 taken off from the water-steam circuit is used for heating the low-CO₂ scrubbing medium or solvent 29, wherein the return S1 of the heat exchanger 24 opens out into the condensate line 14 upstream of the feed water vessel 11 and there condensate returns into the condensate line 14 at a temperature of approximately 120° C. This return point forms a heat source for the condensate flowing in the condensate line 14.

In the region of the heat exchanger 33, the temperature of the CO₂-containing gas conducted in the line 26 is high enough that a temperature of 95° C. can be set in the circuit conducted between the heat exchanger 33 and the heat exchanger WT1 in the flow of the heat exchanger 33 via the line 26.

FIG. 2 shows schematically a power plant 1 which is likewise formed with a CO₂ scrubbing station which is not shown in FIG. 2 with associated CO₂ compression as in the working example according to FIG. 1. To this extent, in FIG. 2, the same reference signs are used for identical and equal parts, elements and components. The important difference from the working example according to FIG. 1 is that now, in addition, a district heating circuit 44 is associated with the power plant 1, the heat requirement of which district heating circuit is substantially fed by the steam lines 45 a-45 d from the water-steam circuit of the power plant 1.

In addition, further plant components in the form of heat exchangers WT3 and WT4 are provided that are used in the district heating circuit 44 as heat sinks. Using the heat exchangers WT3 and WT4, thermal energy is fed back into the district heating circuit 44, which thermal energy was likewise produced at the heat exchangers 33 and 35 used as heat source of the CO₂ scrubbing station with associated CO₂ compression 27 by decoupling or extraction there from the heat stream of the CO₂ scrubbing station. The lines 39, 40 and 41, 43 connecting the heat exchangers WT4 and WT3 to the heat exchangers 33 and 35 can be seen in FIG. 2. Whereas the heat exchanger WT4 is arranged in a bypass line 48 bridging the entire preheating and heating section from a condensate pump 46 to a district heating takeoff point 47, the heat exchanger WT3 is arranged in a bypass line 49 between condensate pump 46 and district heating takeoff point 47 only bridging the first half of the preheating and heating section of the district heating circuit 44. In this case, the interconnection or pipework is such that the heat exchanger 35 downstream of the CO₂ compression station 27 is heat-energy-conductingly connected in the flow thereof to the heat exchanger WT2 via the line 41 as known from the working example according to FIG. 1, the return of which heat exchanger WT2 is connected to the line 43 returning to the heat exchanger 35. Via the line 42, the return of the heat exchanger WT2 is connected to the flow of the heat exchanger WT5, the return of which in turn opens into the line 43. In addition, from line 41, line 50 branches off which forms the flow to the heat exchanger WT4 in the district heating circuit 44, whereas a line 51 connecting to the return of heat exchanger. WT4 opens out into the line 43 leading to the return of the heat exchanger 35. Likewise, in the region of the low-pressure preheating and of the low-pressure preheater 10, again the heat exchanger WT1 is arranged and heat-energy-conductingly connected to the flow line 39 of the heat exchanger 33 at the CO₂ scrubbing station desorber top or regenerator top. Likewise, the return of the heat exchanger WT1 is connected to the return line 40 of the heat exchanger 33. From the flow line 39, a line 52 branches off which leads to the heat exchanger WT3 in the district heating circuit 44, wherein on the return side the heat exchanger WT3 is connected via a line 53 to the return line 40. By this management of heat energy conduction it is possible for thermal energy which is obtained by decoupling using the plant components used as a heat source in the form of heat exchangers 33 and 35 from the heat stream of the CO₂ scrubbing station with associated CO₂ compression not only to be introduced into the heat stream of the power plant 1 in the region of the low-pressure preheater 10 via the heat exchangers WT1, WT2 and WT5, but also to perform in the region of the district heating circuit 44 using the plant components formed there as heat sinks in the form of heat exchangers WT3 and WT4. In this case, the interconnection can be made in various ways. For instance, it is possible to feed alternatively either the heat exchanger WT2 or the heat exchanger WT4 via the heat exchanger 35 and/or alternatively the heat exchanger WT1 or the heat exchanger WT3 via the heat exchanger 33. However, it is also possible in combination to feed in each case the two associated heat exchangers WT2 and WT4 and/or WT1 and WT3 via the corresponding feed lines 41 and 39. Likewise, it is possible to feed the heat exchanger WT5 not only from the return from the heat exchanger WT2 but also from the return of the heat exchanger WT4. In the district heating circuit 44 in this case, downstream of the condensate pump 46, in the region of the branch off of the bypass lines 48, 49, a temperature of 46° C. at 13 bar is achieved, and in the region of the opening out of the bypass line 48 into the district heating circuit 44 a temperature of 136° C. at approximately 14 bar is set. It is natural, depending on the desired arrangement or use of one or more heat exchangers WT1, WT2, WT3, WT4 and/or WT5, to provide in each case only the feed lines or interconnections of lines which are necessary for the desired operation.

FIG. 3 shows, in an extract, a further alternative embodiment which is substantially identical to the embodiment shown in FIG. 2 with the sole difference that the reboiler or evaporator 23 is now no longer fed with the steam D1 from the water-steam circuit, and its return S1 fed to the condensate line 14. Rather, the reboiler 23 is now integrated into the district heating circuit 44, in such a manner that the thermal energy necessary for CO₂ expulsion is provided from the district heating circuit 44 using the tapped-off steam lines 45 a-45 d and also the heat exchangers WT3 and WT4 arranged and interconnected therein as in the working example according to FIG. 2. The same reference signs are again provided for the same or identical parts or elements to the working examples of the preceding FIGS. 1 and 2.

FIG. 4 shows a working example in which the plant components formed as a heat sink in the form of heat exchangers WT6 and WT7 are the only plant components arranged in the district heating circuit 44 for warming/heating up the district heating circuit 44. Therefore, there are no steam feeds 45 a-45 d present, as are present in the working example according to FIG. 3 and the working example according to FIG. 2. Also, the further heat exchangers WT3 and WT4 that are present in the other working examples are no longer present in the district heating circuit 44. In this working example, it is provided that all of the thermal energy decoupled in the region of the CO₂ scrubbing station with associated CO₂ compression 27 is entirely and completely fed to the district heating circuit 44. In this case, the heat exchanger WT6 is connected to the heat exchanger 33 at the CO₂ scrubbing station desorber or regenerator top, which is indicated by the lines 39 and 40. The heat exchanger WT7 is connected to the heat exchanger 35 downstream of the CO₂ compression 27, which is indicated by the lines 41 and 43. In this case, a heat-carrier medium separately present in each case is continuously recirculated in a circuit formed by the lines 41 and 43 between the heat exchangers 35 and WT7, and also a circuit formed by the lines 39 and 40 between the heat exchangers 33 and WT6. Similarly to the embodiment according to FIG. 3, also in the embodiment according to FIG. 4, the heating circuit for the reboiler or evaporator 33 with flow D₂′ and return S₂′ can be integrated into the district heating circuit 44.

Also, if in the embodiments according to FIGS. 1 to 3, in each case a heat exchanger WT5 is arranged and formed downstream of the condensate pump and upstream of the low-pressure preheater 10, there is also the possibility to dispense with such and to feed back the recovered thermal energy solely via at least one or more of the heat exchangers WT1 and/or WT2 and/or WT3 and/or WT4.

In a manner which is not shown, the further heat exchangers 36 of the CO₂ scrubbing station absorber intercooler and/or the heat exchangers 37 of the CO₂ compression intercooler can also form plant components used as heat source in the form of heat exchangers for heat transfer which then are used to interact with one of the plant components WT1-WT7 formed as a heat sink and also the plant components described hereinafter in the form of heat exchangers WT8-WT11.

In the arrangement of the reboiler or evaporator 23 integrated into the district heating circuit 44, the feed from the district heating circuit 44 forms the flow or the evaporator heating D₂′ and the return S₂′ forms the return of the evaporator 23 into the district heating circuit 44.

Instead, for heating the district heating circuit 44, the thermal energy extracted from the heat exchangers 33 and 35 can also be fed into the air preheater or fresh air heater of the fresh air feed to the boiler 2 of the power plant 1 or for coal drying in the coal stream fed to a mill 54, as the further working examples according to FIG. 5 and FIG. 6 show schematically.

FIG. 5 shows a coal feed line 55 leading to the coal mill 54, in the course of which two heat exchangers WT8 and WT9 formed as heat sinks are arranged, wherein the heat exchanger WT8 is connected to at least one of the heat exchangers 36 and/or 37 and the heat exchanger WT9 is connected to at least one of the heat exchangers 33 and/or 35, wherein, in particular, in turn, a heat-carrier medium is circulated through the lines 39, 40 and/or 41, 43. The coal that is fed can be, in particular, brown coal. The heat exchangers WT8 and WT9 are preferably constructed in the form of drum dryers in which the coal stream and the heat-carrier medium stream fed in each case through the lines 39 and 40 are conducted countercurrently separately from one another. As indicated by the dotted line to the heat exchanger WT, still more (or fewer, however) than the two heat exchangers WT8 and WT9 can be arranged in the line 55.

FIG. 6 shows a working example in which heat exchangers WT10 and WT11 are arranged as heat sinks in a fresh air feed (supply) line 56 upstream of the air preheater 57. In this case, the heat exchanger WT10 is in turn connected via lines 39, 40 to the heat exchanger 33 and the heat exchanger WT11 is connected via lines 41, 43 to the heat exchanger 35, wherein in the lines 39/40 and 41/43, in turn a separate heat-carrier medium is circulated. Here also, more or fewer heat exchangers WT can be arranged in the line 56.

The heat exchangers 33 and 35, in the working examples, are designed in such a manner that at the heat exchanger WT1 and the heat exchanger WT3 a flow temperature of the supplied heat-carrier medium of 95° C. is set and a return temperature of the recirculated heat-carrier medium of approximately 50-60° C. is set.

The same temperature level of flow and return is set in the heat carriers WT6, WT8 and WT10.

The temperature management at the heat exchanger 35 is designed in such a manner that, there, a temperature of 185° C. is set as flow of the departing heat-carrier medium stream.

Even if this is not shown in detail, it is also within the scope of the invention to connect each heat exchanger WT1-WT11 forming a heat sink and/or each heat exchanger 33 forming a heat source at the CO₂ scrubbing station desorber top or regenerator top and/or heat exchanger 35 downstream of the CO₂ compression station and/or line 26 and/or line 28 in any desired combination not only with one another but also to connect them together in such a manner that a heat extraction proceeds or is implementable at the heat sources and feeding back with thermal energy to the heat sinks proceeds or is implementable.

FIG. 7 shows a power plant additionally equipped with further recovered energy streams which do not solely consist of energy streams recovered from the region of the CO₂ scrubbing station which are then recirculated to the water-steam circuit. Here, first a heat exchanger WT12 is provided through which the return S₁ flows from the reboiler 23 or the heat exchanger 24 arranged there, wherein the return S₁ then opens out into the condensate line 14 in the direction of flow of the condensate upstream of the feed water vessel 11. Likewise, condensate branched off from the condensate line 14 flows through the heat exchanger WT12 in countercurrent to the reboiler return S₁, which condensate is fed to a further heat exchanger WT13 arranged in a bypass flue gas line 59 of the air preheater 57. The condensate heated by hot flue gas in heat exchanger WT13 flows from there back into the condensate line 14, in the direction of flow of the condensate, upstream of the last heat exchanger in the direction of flow of the condensate of the low-pressure preheater 10.

In the bypass flue gas line 59, a further heat exchanger 14 is arranged, through which condensate likewise flows in countercurrent to the flue gas conducted in the bypass flue gas line 59, which condensate is branched off from the condensate line 14 downstream of the feed water vessel 11 and upstream of the high-pressure heater 13, in the direction of flow of the condensate. After it flows through the heat exchanger 14, the condensate is recirculated back into the condensate line 14 downstream, in the direction of flow of the condensate, of the last heat exchanger of the high-pressure preheater 13. In addition, FIG. 7 also shows the heat exchanger WT10 arranged in the fresh air line 56, which heat exchanger WT10 is connected upstream of the air preheater 57.

The condensate conducted through the heat exchanger WT14 can also open out into the condensate line 14, in the direction of flow of the condensate, downstream of the first heat exchanger of the high-pressure preheater 13.

FIG. 8 shows a similar embodiment in connection with feeding heat into an associated district heating circuit 44 in a development of the working example according to FIG. 2. In addition to the elements already present in the working example according to FIG. 2, here, first, in turn a heat exchanger WT15 fed from the return S₁ of the reboiler 23 is present, after a passage through which the return liquid of the return S₁ opens out into the condensate line 14. Counter-currently thereto, condensate is conducted through the heat exchanger WT15 from the condensate line 14 in a line branching off, in the direction of flow of the condensate, upstream of the last heat exchanger of the low-pressure preheater 10 through the heat exchanger WT15 opening out again into the condensate line 14 likewise in turn, in the direction of flow of the condensate 14, upstream of the last heat exchanger of the low-pressure preheater 10. In parallel to the heat exchanger WT15, a heat exchanger WT16 is arranged through which likewise flows return S₁ of the reboiler 23. Countercurrently to the return S₁, fluid conducted through the heat exchanger WT16 in the district heating circuit 44 is conducted through the heat exchanger WT16.

In addition, in the direction of flow upstream of the branch leading to the heat exchanger WT16, a line 60 branches off from the district heating circuit 44, which line 60 leads to a further heat exchanger WT17 through which flows flue gas conducted in the bypass line 59 countercurrently to the fluid branched off from the heating circuit 44. Via a return line 61, the heat exchanger WT17 is connected to the district heating circuit 44.

In an alternative embodiment to the embodiment of the power plant according to FIG. 8, in the district heating circuit 44, a reboiler takeoff can be provided with flow D′₂ and return S′₂ with branching off from and recirculation to the district heating circuit 44, as shown in FIG. 3. In this embodiment, the feed D₁ to the reboiler 23 and the return S₁ from the reboiler 23 with the heat exchangers WT15 and WT16 integrated therein are then omitted, such as are still present in the working example according to FIG. 8.

In the embodiment according to FIG. 6, feeding in low-temperature heat from the CO₂ scrubbing station/compression 58/27 via the heat exchangers WT10 and WT11 shown there is possible. In this case, in addition, it can also be that the heat exchanger WT10 is connected by pipeline to the heat exchangers 36, 37 of the CO₂ scrubbing station 58 with CO₂ compression 27, and the heat exchanger WT11 to the heat exchanger 33. In this case, there is the possibility of extracting heat at a higher temperature level for the low-pressure or high-pressure preheater 10, 13 or else for a district heating circuit 44. It is possible in this case to provide, via the bypass line 59, on the flue gas side, heat exchanger WT14 and/or heat exchanger WT17, via which condensate branched off from the condensate line 14 and recirculated into the condensate line 14 and/or fluid of the heating circuit 44 branched off from the heating circuit 44 and recirculated back into this can be conducted, as can be seen for the combination WT13 and WT14 in FIG. 7 and the combination of WT14 and WT17 in FIG. 8. The arrangement of a heat exchanger WT13 and/or WT14 and/or WT17 in the bypass flue gas line 59 through which flue gas flows has the advantage that, for maintaining the flue gas stream, no additional fan is necessary, since flow passes through the bypass flue gas line 59 in the direction of the general flue gas flow direction. However, this has the disadvantage that the respective heat exchanger WT13, WT14, WT17 comes into contact with dirty flue gas, for which reason the respective heat exchanger must be fabricated from high-quality steel. In addition, in systems having a denitration system, the risk of forming ammonium bisulfate exists, which precipitates onto the heat exchanger surfaces.

As FIG. 6 additionally shows, it is also possible to provide on the air side a return line 62 in which a further heat exchanger WT18 is arranged which is then pipeline-connected to the condensate line 14 in the region of the low-pressure preheater 10 or the high-pressure preheater 13. The return line 62, in the direction of flow of the fresh air, branches off from the air supply line 56 downstream of the air preheater 57 and opens out again into the fresh air line 56 in the direction of flow of air upstream of the heat displacement system 63. The bypass flue gas line 59 on the flue gas side branches off from the flue gas line 17 in the direction of flow of flue gas upstream of the air preheater 57 and opens out again into the flue gas line 17 in the direction of flow of flue gas downstream of the air preheater 57 and upstream of the heat displacement system 63. In the return line 62, a fan 64 is arranged in order to be able to move the fresh air recirculated therein against the general direction of flow of the fresh air in the line 56.

In addition to the direct heating of the heat exchanger 24 of the reboiler 23 using steam branched off from the steam circuit in the flow line D₁ with reboiler return S₁, it is also possible to heat the heat exchanger 24 indirectly with steam. This is shown in FIG. 9. In this case, in a heat-carrier medium circuit 65, in which the heat exchanger 24 of the reboiler 23 is arranged, a heat-carrier medium is circulated. On the flow section to the heat exchanger 24, in the heat-carrier medium circuit 65, three heat exchangers 66, 67 and 68 are arranged which are heated with supplied steam, more precisely, for example, fresh steam to the heat exchanger 66, medium-pressure steam to the heat exchanger 67 and low-pressure steam to the heat exchanger 68, wherein the steam is taken off from the water-steam circuit of a power plant 1 according to the designation D₁. This indirect (warm water) heating of the reboiler 23 by way of the heat-carrier medium circuit 65 reduces the risk, compared with direct and immediate steam heating, that the feed water is contaminated with the chemical absorption medium 29 due to possible leaks in the reboiler heat exchanger 24. In this case, by arranging the heat exchangers in the direction of flow of the heat-carrier medium water conducted in the heat-carrier medium circuit 65 in the sequence heat exchanger 68, heat exchanger 67, and then heat exchanger 66, a stepwise heating is provided.

A Rankine cycle can also be supplied with low-temperature heat from the CO₂ scrubbing station/CO₂ compression 58/27, as FIG. 10 shows. In this case, two heat exchangers WT19 and WT20 are arranged in a Rankine cycle 69, in particular in an organic Rankine cycle. In the Rankine cycle, by way of an organic solvent or preferably ammonia (NH₃), a circuit is operated in which low-temperature waste heat from the CO₂ scrubbing station 58/CO₂ compression 27 is used. In the working example, the heat exchanger WT19 is arranged in the “cold step” of the Rankine cycle 69 and waste heat is fed thereto from the absorber intercooler 36 or the CO₂ compression intercooler 37. By way of the heat exchanger WT20, which is arranged in the “hot step” of the Rankine cycle 69, waste heat which is not required in the CO₂ scrubbing station from the desorber top, i.e. thermal energy obtained via the heat exchanger 33, or thermal energy from the CO₂ compression, i.e. thermal energy produced via the heat exchanger 35, is fed to the Rankine cycle 69. The consumer 75 associated with the turbine step of the Rankine cycle 69 can be a generator for power generation, or else a mechanical drive of a feed pump or of a CO₂ compressor. Even if in the working example according to FIG. 10, both a heat exchanger WT19 and a heat exchanger WT20 are provided, it is also possible, depending on the design of the power plant, to provide only one of the two heat exchangers WT19 or WT20.

Of course, it is also possible, instead of the respective heat exchangers WT1-WT20 shown in FIGS. 1-10, to provide in each case a plurality of series- or parallel-connected heat exchangers of one type. This depends on the desired dimensioning of the respective heat exchangers and is within the discretion of the person skilled in the art.

FIGS. 11 and 12 show the use of a heat exchanger WT21 which, on the flue gas side, takes up thermal energy from the flue gas flowing through the bypass flue gas line 59, wherein the bypass flue gas line 59 is a plant component utilized as heat source. The heat exchanger WT21 releases the absorbed heat to the flow D₃ leading to the heat exchanger 24 of the reboiler 23, wherein the heat-carrier medium is recirculated to the heat exchanger WT21 from the heat exchanger 24 via the reboiler return S₃. To this extent, the heat exchanger WT21 is designed as a plant component fed on the flue gas side and used as a heat source, and then the heat exchanger 24 associated with the reboiler 23 is a plant component used as a heat sink.

The working example according to FIG. 12 differs from the working example according to FIG. 11 only in that here a heat exchanger WT11 fed from the heat exchangers 37 of the intercooler of the compressor 27 is arranged in the fresh air line 56 upstream, in the direction of flow of the air, of the heat displacement system 63, which heat exchanger WT11 therefore represents as plant component a heat sink fed from the CO₂ compression 27.

FIG. 11 shows a flue gas line 17 which, in the direction of flow of the flue gas, leads downstream of a denitration system 70 to the air preheater 57 and thereafter to an electrostatic precipitator 71. On the path between the denitration system 70 and the electrostatic precipitator 71, the bypass flue gas line 59 that branches off from the flue gas line 17 and opens out again into it bypasses the air preheater 57, but opens out again into the flue gas line 17 upstream of the electrostatic precipitator 71. Downstream of the electrostatic precipitator 71, a heat displacement system 63 is arranged in the flue gas line 17, in which heat displacement system are arranged two heat exchangers 73 and 74 that are connected to one another via a circulated heat-carrier medium, of which heat exchangers, thermal energy is taken off from the flue gas stream conducted in the line 17 by the heat exchanger 73, and given off to the heat-carrier medium circulated in the heat displacement system 63. Downstream of the heat displacement system 63 is then, in addition, a further flue gas desulfurization system 72 which is then followed by the CO₂ scrubbing station 58 comprising the absorber 20 with associated desorber 22 for CO₂ separation, before the low-CO₂ exhaust gas 21 then leaves the plant. In addition, the fresh air line 56 is provided, which, in the direction of flow of fresh air, upstream of the air preheater 57, is first passed through the heat displacement system 63 and there, in the heat exchanger 74, takes up the thermal energy given off by the flue gas via the heat exchanger 74 to the heat carrier medium circulated in the heat displacement system 63. In the 800-850 MW_(el) power plant underlying this embodiment, in the heat displacement system 63, the low-temperature heat present upstream of the flue gas desulfurization system 72 is transferred to the fresh air stream upstream, in the direction of flow of fresh air, of the air preheater 57. The fresh air stream that is preheated thereby, in the air preheater 57, then requires only a relatively small heat energy supply, in order to have the temperature envisaged downstream of the air preheater 57 in the direction of flow. This is used for passing the amount of heat which, although it is present in the flue gas, is then no longer required for heating the fresh air in the air preheater 57, via the bypass flue gas line 59 and there, in the heat exchanger WT18, to transfer it to the heat-carrier medium ZM passed therein and as flow D₃ to the heat exchanger 24 of the reboiler 23. By this means, to this heat-carrier medium, sufficient energy can be provided to be fed to the reboiler 23 that the heat-carrier medium has a temperature of above 120° C. to a maximum of 360° C. In this manner, approximately 60 MW_(th) can be obtained, whereby, by way of the attached CO₂ separation system (CO₂ scrubbing station/CO₂ compression), the efficiency loss can be decreased by 1.5% compared with a plant without such a CO₂ separation system.

A further 12 MW may be obtained, in the embodiment according to FIG. 12, by the heat exchanger WT11 fed from the intercooler 37 of the CO₂ compression 27 being heated to a temperature of below 60° C. such that the heat displacement system 63 can develop undiminished its complete intended action, but nevertheless the fresh air in this case is already preheated, in such a manner that in the air preheater 57, less thermal energy only need be taken off from the flue gas, in such a manner that an increased amount of thermal energy is available in the bypass flue gas line 59. In this manner 72 MW_(th) can be obtained in the heat exchanger WT18.

Overall, in the various working examples, therefore, the heat exchanger 33, the line 26, the heat exchanger 35, the line 28, the heat exchanger 36 and the heat exchanger 37 are formed as plant components utilized as a heat source and are arranged in a power plant, wherein these heat sources are fed with thermal energy present in the region of the CO₂ scrubbing station 58 with associated CO₂ compression 27 or thermal energy which is produced there. Plant components used as heat sinks which release again thermal energy fed in from the existing heat sources, that is to say from the region of the CO₂ scrubbing station 58 with associated CO₂ compression 27, are the heat exchangers WT1-WT12, and also the heat exchangers WT15 and WT16. In this case the heat exchangers WT1, WT2, WT5, WT12 and WT15 feed the thermal energy obtained from the CO₂ scrubbing station 58 with associated CO₂ compression 27 into the steam-water circuit of the power plant 1. The heat exchangers WT3, WT4, WT6, WT7 and WT16 feed the thermal energy obtained into the district heating circuit 44. The heat exchangers WT8 and WT9 feed the thermal energy obtained or taken up into the coal line 55 leading to the coal mill 54. The heat exchangers WT10 and WT11 feed the thermal energy obtained or taken up into the fresh air line 56. The heat exchangers WT19 and WT20 that are likewise fed with thermal energy from the CO₂ scrubbing station 58 with associated CO₂ compression 27 release the thermal energy taken up to the Rankine cycle 69 in their function as heat sink.

Plant components taking up flue gas thermal energy from the flue gas side, i.e. conducted in the bypass flue gas line 59 that have the function of a heat source are, in addition, the heat exchangers WT13, WT14, WT17 and WT21, wherein the heat exchangers WT13 and WT14 feed in the thermal energy taken up into the plant component of the water-steam circuit of the power plant 1, to this extent forming a heat sink, and the heat exchanger WT17 gives off the thermal energy taken up into the district heating circuit 44 as the plant component forming the associated heat sink. The heat exchanger WT21 gives off the heat taken up to the flow D₃ to the heat exchanger 24 of the reboiler 23, in such a manner that the heat exchanger 24 likewise develops the function of a plant component having a function as a heat sink giving off thermal energy to the CO₂ scrubbing station.

The heat exchanger WT18 forms a heat source fed immediately by the thermal energy of the fresh air leaving the air preheater 57, but thereby indirectly a heat source fed by thermal energy from the region of the CO₂ scrubbing station 58 and/or CO₂ compression 27, since heat taken off from the region of the CO₂ scrubbing station 58 and/or CO₂ compression 27 is fed back or fed into the fresh air via the heat exchangers WT10 and/or WT11 upstream of the return line 62, in the direction of flow of the air. The heat source WT18 releases the heat taken up to the condensate line 14 acting as a heat sink in the region of the low-pressure preheater and/or the high-pressure preheater 10 and/or 13 at the water-steam circuit of the power plant 1.

The present invention relates to a method for the “optimal” integration of heat streams into a conventional power plant process. The conventional power plant process can be all known fossil-fired power plant processes. In particular, it is a hard-coal-fired power plant process in the net output range between 500 and 1000 MW_(el). In the working example, it is a hard-coal-fired power plant process having a net output of approximately 850 MW_(el). The heat streams that are to be integrated can be in a temperature range between 50 and 400° C. In particular, the heat energies to be integrated are in a temperature range between 50 and 200° C. The source of the heat streams can be systems for obtaining solar heating or geothermal energy or can be systems which are in direct link to said conventional power plant process. The systems which are in a direct link to said conventional power plant process can be waste heat streams which originate from a fuel drying system. In particular, the waste heat streams can originate from a chemical CO₂ scrubbing station having an absorber and desorber system and subsequent compression of the separated carbon dioxide connected downstream of the power plant process.

In the working example, a conventional hard-coal-fired power plant block having a net output of 850 MW_(el) is assumed. This hard-coal-fired power plant block has a gross electrical efficiency of 47.83% and a net electrical efficiency of 45.25%. The in-house electrical consumption is approximately 40 MW_(el), with the feed pump being electrically driven. With a chemical CO₂ scrubbing station/compression 58/27, the power plant block, without recirculation of the waste heat, has a gross electrical efficiency of 32.42% and a net electrical efficiency of 32.86% at an in-house electrical consumption of 93 MW thermal. The power plant block optionally offers the possibility of extracting district heat 44. In addition, the preheating section of the water/steam circuit consists of five low-pressure preheaters 10 and three high-pressure preheaters 13. The temperatures of the fuel, the fresh air and the cooling water are assumed to be 15° C. For a hard-coal-fired 850 MW_(el) power plant block, for the full load case, for a CO₂ scrubbing station for the entire flue gas, at a degree of separation of 95%, a heat stream of at least 510 MW_(th) is required at a temperature level between 120 and 170° C. In this case, it is assumed that the specific total energy requirement for the CO₂ scrubbing station in an absorber and desorber system is 3600 kJ (kg of CO₂). This requirement corresponds to values for the scrubbing medium monoethanolamine (MEA) known in this respect, at a concentration of 30% in water. The required process heat for the chemical CO₂ scrubbing station is taken off from the power plant process in a suitable manner D1 via a collector system between the various turbine stages 3, 4, 5. It is of importance in the takeoff of process steam from the water/steam circuit that the pressure differences of the subsequent turbine stages remain in the material-specific limits. It is the purpose of the present invention to minimize the loss of efficiency of the overall process which is caused by the high demand of thermal energy in the chemical CO₂ scrubbing station. For this reason, additional heat exchangers are installed in the water-steam circuit of the conventional power plant, in which heat exchangers, at a suitable point and at a suitable temperature level, waste heat from the CO₂ scrubbing station system and the CO₂ compression is recirculated and therefore an improved efficiency for the overall system is achieved. A further purpose is to keep as low as possible the demand for cooling water which is increased by the chemical CO₂ scrubbing station/compression 58/27. That is to say, the more heat can be recirculated from the CO₂ scrubbing station/compression 58/27 to the conventional water-steam circuit, the less additional cooling capacity (cooling tower capacity) need be installed.

The CO₂ scrubbing station is an absorber 20 and desorber 22 system in which the CO₂ is separated off from the flue gas stream by chemical absorption. In the chemical absorption, owing to the chemical reaction, heat is liberated which is removed by intercoolers 26 to achieve a better degree of conversion. The loaded scrubbing medium then arrives in the desorption column 22 in which the energy is fed via a reboiler 23 which is required for breaking the chemical bond between the scrubbing medium and the CO₂. In addition, the water loading of the CO₂ that is liberated again at the desorber top, owing to the higher temperature, is higher than that of the flue gas treated in the absorber 20, and so for this purpose likewise energy must be supplied. Overall requirement 3600 kJ/(kg of CO₂) for in MEA/water ratio of 30/70. The temperature which is necessary in the desorption column 22 for breaking the chemical bond is, in the described system, about 120° C. At the desorber top, this gives a completely water-saturated CO₂ stream which has a temperature of about 115° C. After cooling the CO₂ and associated condensation of the entrained water, CO₂ compression can proceed. In the working example according to FIG. 1, the CO₂ is compressed to 200 bar in a nine-stage compression. In this case, owing to an energy-efficient compression between the first seven stages, in each case an intercooler 37 is connected intermediately. The intercooling takes place at a temperature level of about 65 to 30° C. The last compression stages are connected in series without intercooling. Then, the compressed CO₂ stream has a temperature of about 190° C. This temperature is too high for further processing of the CO₂, and so further cooling 35 is necessary. Then, the CO₂ is at approximately 25° C./200 bar and in the liquid state.

Plant components that are usable as “heat source” are:

-   -   The CO₂ exiting at the top of the desorber 22 is completely         saturated with water and, at a pressure of approximately 2 bar,         has a temperature of about 115° C. At a mass flow rate of         approximately 250 kg/s, approximately 40% water is present. With         a separate water circuit, a water mass flow rate of         approximately 1050 kg/s can be heated up to about 105° C. For         heating up such a water mass flow rate, the heat exchanger 33 is         the plant component usable as “heat source”. However, the line         26 can also act as a heat source. The plant components used as         “heat sink” heat exchangers WT1 and/or WT3 and/or WT6 and/or         WT10 and/or WT9 can be operated with the water mass flow rate. A         further advantage is that the water-saturated CO₂ in any case         needs to be cooled before the compression and needs to be freed         from a majority of the water. In the full load case, the CO₂ can         be lowered to a temperature of 60° C. and a water content of 4%         using said heat exchangers WT1 and/or WT3 and/or WT6 and/or WT9         and/or WT10.     -   The CO₂ compressed in the CO₂ compression 27 at 200 bar and         190° C. needs to be condensed or cooled for further processing.         The CO₂ mass flow rate is approximately 150 kg/s. The plant         components heat exchangers WT2 or, alternatively, WT4 or WT7 and         WT5 or WT9 used as a “heat sink” can be operated using this CO₂         mass flow rate. Plant components used as a “heat source” are in         this case the heat exchanger 35 and/or the line 28.     -   In the intercooling of the CO₂ compression 27, the CO₂ is cooled         from approximately 65° C. down to approximately 35° C. The plant         components used as a “heat sink” heat exchangers WT8 and/or WT11         can be operated therewith. In this case the heat exchangers 37         are used as plant components forming “heat sources”.     -   In the intercooling of the absorber 20, the scrubbing solution         which, owing to the heat of absorption, warms up to         approximately 60° C., is cooled down again to approximately         40° C. in order to improve the CO₂ absorption capacity of the         scrubbing solution. This cooling proceeds by way of the plant         components used as a “heat source” heat exchanger 36. The plant         components used as a “heat sink” heat exchangers WT8 and/or WT11         can be operated with the thermal energy obtained thereby.     -   The return 31 of the reboiler has a temperature of approximately         120° C. The mass flow rate of warm water is approximately 220         kg/s. The heat exchangers WT12 and/or WT15 and/or WT16 can be         operated therewith. The heat exchanger 24 in this case (FIG. 7         and FIG. 8) is a plant component used as a “heat source”.

In the working example of a hard-coal-fired 850 MW_(el) power plant block, the following serve as “heat sinks”:

-   -   The LP preheating section 10 having a temperature range from 20         to 120° C. Here, the heat exchangers WT1, WT2, WT5, WT12 and         WT15 are added.     -   The HP preheating section 13 having a temperature range from 160         to 290° C. Here, the heat exchanger WT14 is added. This is a         special case, since here heating is not directly from CO₂         scrubbing station/compression, but from an air preheater bypass         59 which is possible via WT10.     -   The district heat extraction system having a temperature range         from 46 to 136° C. Here, the heat exchangers WT3, WT4 and WT16         are added.     -   The fresh air preheater, wherein the fresh air, depending on the         time of year, is at a temperature between −10 and 30° C. Here,         the heat exchanger WT10 is added.     -   In the case of a partial treatment of the flue gas, the         recyclable amounts of heat from the CO₂ scrubbing         station/compression are lower, and so in this case also waste         heat from the absorber inter-cooler 36 or the compression         intercooler 37 in the heat exchanger WT11 needs to be used.     -   The drying system for the fuel (in the case of brown coal),         wherein the fuel is at an entry temperature of 15° C. Here, the         heat exchanger WT9 is added. In the case of a partial treatment         of the flue gas, the recyclable amounts of heat from the CO₂         scrubbing station/compression are lower, and so waste heat from         the absorber intercooler 37 or from the compression intercooler         36 needs to be used in the heat exchanger WT8.

WT1 transfers heat from a substream 33 of the desorber top heat to the LP preheating section 10. Here, approximately 50% (100% at 200 MW district heat extraction) of the incoming condensate is warmed from 20 (29° C. at 200 MW district heat extraction) to 100° C. In this case approximately 32 MW (approximately 60 MW at 200 MW district heat extraction) are transferred to the water-steam circuit. The increase in efficiency via this heat exchanger WT1 is 0.38% point (0.79% point for 200 MW district heat extraction).

WT2 transfers heat 25 from the last stage of the CO₂ compression to the LP preheating section 10. Here, approximately 50% of the incoming condensate is heated from 20 to 120° C. In this process approximately 49 MW are transferred to the water-steam circuit. The increase in efficiency due to this heat exchanger WT2 is 1.19% points. This heat exchanger is alternatively used for WT4 which is only used when district heat 44 is extracted.

WT3 transfers heat 33 from a substream of the desorber top heat to the district heating circuit 44. Here, approximately 60% of the district heating return is heated from 46° C. to 100° C. In this process approximately 80 MW are transferred to the district heating circuit 44. The increase in efficiency due to this heat exchanger WT3 is 1.70% points.

WT4 transfers heat 35 from the last stage of the CO₂ compression 27 to the district heating circuit 44. Here, approximately 20% of the district heating return is heated from 46° C. to 136° C. In this case approximately 40 MW are transferred to the district heating circuit 44. The increase in efficiency due to this heat exchanger WT4 is 1.36% points. This heat exchanger is alternatively used for WT2 which is only used when no district heat is extracted.

WT5 transfers heat 35 from the last stage of the CO₂ compression 27 to the LP preheating section 10. The heat exchanger WT5, however, is not fed directly from the CO₂ compression, but preferably from the return from WT4. The heat exchanger WT5 is therefore, preferably, only used when the heat exchanger WT4 is operating, that is to say when district heat is extracted. The reason for this is that the return from WT4 is, at approximately 50° C., markedly higher than that from WT2 at 25° C., and therefore is still suitable both for further cooling the compressed CO₂ stream and also for heating up 100% of the condensate from 20 to 30° C. In this case approximately 10 MW are transferred to the condensate upstream of the LP preheaters. The increase in efficiency due to this heat exchanger is 0.36% point.

WT6 transfers heat 33 from a substream of the desorber top heat to the district heating circuit 44. Here, in the embodiment according to FIG. 4, a district heat generation is considered which is exclusively fed with waste heat from the CO₂ scrubbing station/compression 58/27. In this process approximately 30 MW are transferred to the district heating circuit 44.

WT7 transfers heat 35 from the last stage of the CO₂ compression 27 to the district heating circuit 44. Here (FIG. 4), a district heat generation is considered which is exclusively fed with waste heat from the CO₂ scrubbing station/compression 58/27. In this process approximately 20 MW are transferred to the district heating circuit.

WT10 transfers heat 33 from a substream of the desorber top heat to the fresh air 50. In this process approximately 57 MW of heat are transferred to the fresh air which enters at a mass flow rate of approximately 640 kg/s at 15° C. and exits at 100° C. The increase in efficiency due to this heat exchanger is 1.22% points (1.16% points at 200 MW district heat extraction).

The heat exchanger WT11 can be operated in two ways: a) by way of waste heat (36) from the absorber inter-cooler, or b) by way of the compression intercooler 37. In both ways, WT11 is used with a flow temperature of approximately 60° C. This heat exchanger WT11 can be used if only a small substream of the flue gas is treated in the CO₂ scrubbing station/compression 58/27. The recyclable amount of heat from the CO₂ scrubbing station/compression 58/27 is thereby lower, and so waste heat from the absorber intercooler 36 or the compression intercooler 37 needs to be used in WT11.

WT14 is operated using an air preheater bypass 59. This heat exchanger WT14 can be used, since, owing to WT10, the fresh air enters the air preheater 57 approximately 85° C. hotter. The air preheater exit temperature of the fresh air is, however, limited to 340° C., and so here, by the air preheater bypass 59, heat at a higher temperature level must be taken off. In this heat exchanger WT14, approximately 150 kg/s of flue gas is cooled from 380° C. to 170° C. On the other hand, by way of this amount of heat, approximately 200 kg/s of water can be heated from 160° C. to 205° C. This mass flow rate of water is used for bridging the first HP preheater of the high-pressure heater 13. With this heat exchanger WT14, approximately 40 MW are transferred. The increase in efficiency due to this heat exchanger WT14 is 1.3% points (likewise at 200 MW of district heat also).

The heat exchanger WT16 transfers heat 35 from the reboiler return S1 to the district heating circuit 44. Here, the entire district heating mass stream is heated from 95° C. to 105° C. The reboiler return S1 is cooled in this process from approximately 120° C. to 100° C. Approximately 20 MW of heat are transferred in this case. The heat exchanger is used between the third and fourth heat exchanger of the district heating circuit 44 having in each case four heat exchangers in the working example of FIGS. 2, 3, 7 and 8, and considerably reduces the requirement of cold intermediate superheated steam. The increase in efficiency due to the heat exchanger WT16 is 0.90% point.

The heat exchangers WT12 and WT15 transfer heat from the reboiler return S1 to the LP preheating section. Here, preferably, the entire mass stream heated in WT1 to 100° C. is heated to 116° C. The reboiler return is cooled in this process from approximately 120° C. to 110° C. In this case approximately 8 MW of heat are transferred. These heat exchangers WT12 and WT15 are used both between the fourth and fifth heat exchangers of the LP preheating section of the low-pressure preheater 10 having in each case five heat exchangers in the working examples of FIGS. 1, 2, 7 and 8, and reduce the requirement for MP steam. The increase in efficiency due to this heat exchanger is 0.4% point.

WT9 transfers heat from: a) a substream of the desorber top heat 33 and b) the last stage of the CO₂ compression 35, to the fuel in order to preheat it starting from 15° C.

The heat exchanger WT8 can be operated in two ways: a) by way of waste heat from the absorber intercooler 36 or b) by way of the compression intercooler 37. In both ways, WT8 is used at a flow temperature of approximately 60° C.

Proceeding from a power plant 1 having a 200 MW thermal district heat extraction without the waste heat utilization according to the invention, a gross electrical overall efficiency of 31.4% and a net efficiency of 25.91% for an in-house electrical demand of 94 MW can be assumed. If, in such a power plant, the heat exchangers WT1, WT2, WT10, WT14 and WT12 or WT15 are used and are in operation, the gross overall efficiency of the power plant block including the complete CO₂ scrubbing station/CO₂ compression due to the feeding back in of the heat is 43.13% for a net efficiency of 37.42% and an in-house electrical demand of approximately 93 MW. In comparison with an identical power plant without a CO₂ scrubbing station, this means an overall net loss of efficiency of 7.83% points, wherein due to the feeding back in of heat according to the invention, this overall net loss of efficiency is reduced by 4.56% points, due to use of the CO₂ scrubbing station/compression, therefore only an overall net loss of efficiency of 3.27% points occurs.

In a power plant having district heat extraction, in which then the heat exchangers WT1, WT3, WT4, WT5, WT10, WT14 and WT16 are used and in operation, then an electrical overall gross efficiency of the power plant block with complete CO₂ scrubbing station/compression and feeding back in of the heat at 200 MW thermal heat extraction of 39.31% may be achieved. The net efficiency is then 33.64% for an electrical in-house demand of 93 MW. The overall net efficiency of such an overall plant is then 7.73% points above that of an identical process without feeding back waste heat according to the invention.

The method according to the invention and/or the power plant 1 according to the invention can also be designed in such a manner that heat from solar-heating and/or geothermal heat sources WT1, WT2, WT5 is used or is usable for low-pressure preheating, for heating a district heating circuit WT3, WT4 associated with the power plant 1 and/or for fresh air preheating WT10, WT11 with associated air preheater bypass 59 for a heat displacement in a heat stream in the region of the water-steam circuit of the power plant 1, in particular in the low-pressure and/or high-pressure preheater, and/or a district heating circuit associated with a power plant 1, preferably in combination with a CO₂ scrubbing station 58. 

1. A method for heat recovery by connecting a plurality of heat streams of a fossil-fired power plant to a CO₂ scrubbing station which is downstream of the combustion and is for the flue gas by means of chemical absorption and/or desorption and associated CO₂ compression, wherein from the heat stream of the CO₂ scrubbing station with associated CO₂ compression, thermal energy in the form of at least one heat substream is extracted and fed back into a heat stream that is coupled directly or indirectly to the heat stream of the boiler or steam generator of the power plant and/or wherein from the flue gas heat stream, thermal energy in the form of at least one heat substream is extracted and fed back into the heat stream of the CO₂ scrubbing station with associated CO₂ compression.
 2. The method as claimed in claim 1, wherein thermal energy available in the region of the CO₂ scrubbing station with associated CO₂ compression is decoupled or extracted from the heat stream of the CO₂ scrubbing station with associated CO₂ compression as a heat substream by at least one first plant component that is utilizable there as a heat source, and/or thermal energy available in the region of a flue gas line is decoupled or extracted from the heat stream of the flue gas by at least one second plant component that is utilizable there as a heat source and the thermal energy in the region of the power plant obtained respectively by the decoupling or extraction in the form of the at least one heat substream is fed back into the heat stream of the power plant outside the respective decoupling or extraction region by at least one further plant component that is utilizable there in each case as heat sink for the thermal energy obtained.
 3. The method as claimed in claim 1, wherein thermal energy available in a CO₂-rich gas stream and/or in the absorption medium used is decoupled or extracted in the region of the CO₂ scrubbing station with associated CO₂ compression.
 4. The method as claimed in claim 1, wherein thermal energy available in the flue gas is decoupled or extracted in the region of the flue gas line and/or in the region of a bypass flue gas line bypassing an air preheater.
 5. The method as claimed in claim 1, wherein the thermal energy that is decoupled or extracted in the region of the CO₂ scrubbing station with associated CO₂ compression is fed back into the heat stream of the power plant outside the region of the CO₂ scrubbing station with associated CO₂ compression.
 6. The method as claimed in claim 1, wherein the thermal energy which is decoupled or extracted in the region of the flue gas line and/or in the region of the bypass flue gas line is fed back into outside the region of the flue gas line and/or the bypass flue gas line the water-steam circuit and/or the district heating circuit and/or the region of the CO₂ scrubbing station with associated CO₂ compression.
 7. The method as claimed in claim 1, wherein the thermal energy is decoupled or extracted by one or more heat sources formed at the CO₂ scrubbing station desorber or regenerator head and/or downstream of the CO₂ compression in the CO₂ flow direction and/or in the region of the CO₂ scrubbing station absorber intercooler and/or in the region of the CO₂ compression intercooler, and the thermal energy is fed back in by means of one or more heat sinks formed in the region of the low-pressure preheater and/or in the condensate flow direction upstream of the low-pressure preheater and/or in a district heating circuit and/or in a fresh air heater and/or in a coal drying station and heat-energy-conductingly connected to the heat source(s).
 8. The method as claimed in claim 1, wherein the thermal energy is decoupled or extracted by one or more heat sources formed in the flue gas line and/or in the bypass flue gas line and the thermal energy is fed back into the water-steam circuit in the region of the low-pressure preheater and/or the high-pressure preheater and/or into the district heating circuit and/or into the region of the CO₂ scrubbing station.
 9. The method as claimed in claim 1, wherein the thermal energy which is decoupled or extracted in the region of the CO₂ scrubbing station with associated CO₂ compression is fed back into the heat stream of the power plant by heat exchangers arranged in a Rankine cycle.
 10. The method as claimed in claim 1, wherein the method is carried out in a power plant as claimed in claim
 11. 11. A power plant having a CO₂ scrubbing station which is downstream of the combustion and is for the flue gas by chemical absorption and/or desorption and associated CO₂ compression, wherein at least one first plant component that is utilized as a heat source and which effects the decoupling or extraction of thermal energy from the heat stream of the CO₂ scrubbing station with associated CO₂ compression is arranged and/or is formed in the region of the CO₂ scrubbing station with associated CO₂ compression and/or at least one second plant component that is utilized as a heat source and which effects the decoupling or extraction of thermal energy from the flue gas stream is arranged and/or formed in the region of a flue gas line and/or a bypass flue gas line bypassing an air preheater, and at least one third plant component that is heat-energy-conductingly connected to said plant component and is also utilized as a heat sink and effects the feeding back into of the decoupled or extracted thermal energy the heat stream of the power plant outside the respective decoupling or extraction region is arranged and/or formed in the region of the power plant.
 12. The power plant as claimed in claim 11, wherein one or more of the first plant components utilized as heat source(s) for heat transfer is/are arranged and/or formed at the CO₂ scrubbing station desorber or regenerator head and/or downstream of the CO₂ compression in the CO₂ flow direction and/or in the region of the CO₂ scrubbing station absorber intercooler and/or in the region of the CO₂ compression intercooler, each of which first plant components is heat-energy-conductingly connected in a manner bearing a heat-carrier medium to one or more plant components arranged in the region of the low-pressure preheater and/or in the condensate flow direction upstream of the low-pressure preheater and/or in a district heating circuit and/or in the fresh air heater and/or in the coal drying station and, as heat sink(s), effecting a heat transfer.
 13. The power plant as claimed in claim 11, wherein at least one first plant component forming a heat source is formed and is connected in the manner heat-energy-conductingly bearing a medium to at least one further plant component arranged in the region of the power plant forming a heat sink wherein one or more of the first plant components selected from a heat exchanger at the CO₂ scrubbing station desorber or regenerator head and/or a heat exchanger downstream of the CO₂ compression and/or a heat exchanger of the CO₂ scrubbing station absorber intercooler and/or a heat exchanger of the CO₂ compression intercooler each forms a heat exchanger acting as a heat source, and/or a line conducting high CO₂-content gas downstream of a desorber forms a plant component utilized as a heat source, and/or a line conducting liquid CO₂ downstream of the CO₂ compression forms a plant component utilized as a heat source, and also one or more of the further plant components selected from a heat exchanger of the low-pressure preheater and/or a heat exchanger upstream of the low-pressure preheater and/or a heat exchanger in the district heating circuit and/or a heat exchanger of the coal drying station and/or a heat exchanger of the fresh air heater each forms a further heat exchanger acting as heat sink.
 14. The power plant as claimed in claim 11, wherein the heat exchanger forming a heat source at the CO₂ scrubbing station desorber or regenerator head is heat-energy-conductingly connected to a heat exchanger, forming a heat sink, of the low-pressure preheater.
 15. The power plant as claimed in claim 11, wherein the heat exchanger forming a heat source is heat-energy-conductingly connected downstream of the CO₂ compression to a heat exchanger, forming a heat sink, of the low-pressure preheater.
 16. The power plant as claimed in claim 11, wherein the heat exchanger, upstream of the low-pressure preheater, is arranged in a condensate line downstream in the condensate flow direction of a condensate pump, and/or the heat exchangers of the low-pressure preheater are arranged in a bypass line branching off from the condensate line.
 17. The power plant as claimed in claim 11, wherein the return of the heat exchanger of the low-pressure preheater is heat-energy-conductingly connected to the flow of the heat exchanger upstream of the low-pressure preheater.
 18. The power plant as claimed in claim 11, wherein a heat-carrier medium is conducted in a circuit formed by the heat exchanger downstream of the CO₂ compression, the heat exchanger next to a feed water container in the condensate flow direction and the heat exchanger upstream of the low-pressure preheater and/or is conducted in a circuit formed by the heat exchanger at the CO₂ scrubbing station desorber or regenerator head and the heat exchanger next to a condensate pump positioned in the upstream-side condensate flow direction, in each case through these heat exchangers.
 19. The power plant as claimed in claim 11, wherein the heat exchanger at the CO₂ scrubbing station desorber or regenerator head and/or the heat exchanger downstream of the CO₂ compression is/are heat-energy-conductingly connected to one or more heat exchangers arranged in the district heating circuit.
 20. The power plant as claimed in claim 19, wherein one or more of the heat exchangers arranged in the district heating circuit is/are heat-energy-conductingly connected to one or more of the heat exchangers associated with or arranged upstream of the low-pressure preheater.
 21. The power plant as claimed in claim 19, wherein the heat exchanger upstream of the low-pressure preheater is arranged in the return of the heat exchanger arranged in the district heating circuit and/or in the return of the heat exchanger associated with the low-pressure preheater.
 22. The power plant as claimed in claim 11, wherein the heat energy supply for the reboiler or evaporator is constructed to be integrated into the district heating circuit.
 23. The power plant as claimed in claim 11, wherein the heat exchanger at the CO₂ scrubbing station desorber or regenerator head and/or the heat exchanger downstream of the CO₂ compression is/are heat-energy-conductingly connected to one or more heat exchangers arranged in a power plant coal line connected to a coal mill.
 24. The power plant as claimed in claim 11, wherein the heat exchanger at the CO₂ scrubbing station desorber or regenerator head and/or the heat exchanger downstream of the CO₂ compression is/are heat-energy-conductingly connected to one or more heat exchangers arranged in a fresh air line feeding fresh air to the boiler of the power plant.
 25. The power plant as claimed in claim 11, wherein at least one heat exchanger arranged in the bypass flue gas line is heat-energy-conductingly connected to the water-steam circuit of the power plant in the region of the low-pressure preheater or the high-pressure preheater.
 26. The power plant as claimed in claim 11, wherein a heat exchanger arranged in the bypass flue gas line is heat-energy-conductingly connected to the district heating circuit.
 27. The power plant as claimed in claim 11, wherein a heat exchanger arranged in the bypass flue gas line is heat-energy-conductingly connected to the reboiler and/or to a heat exchanger of the reboiler.
 28. The power plant as claimed in claim 11, wherein a heat exchanger heat-conductingly connected to the district heating circuit and/or a heat exchanger heat-conductingly connected to the water-steam circuit of the power plant is arranged in the reboiler return.
 29. The power plant as claimed in claim 11, wherein the heat exchanger at the CO₂ scrubbing station desorber or regenerator head and/or the heat exchanger downstream of the CO₂ compression and/or the heat exchanger of the CO₂ scrubbing station absorber intercooler and/or the heat exchanger of the CO₂ compression intercooler is/are heat-conductingly connected to a heat exchanger arranged in a Rankine cycle.
 30. The method for heat recovery as recited in claim 1, wherein the fossil-fired power plant comprises a coal-fired power plant.
 31. The method as recited in claim 5, wherein the thermal energy that is decoupled or extracted in the region of the CO₂ scrubbing station with associated CO₂ compression is fed back into the heat stream of the power plant into the water-steam circuit and/or a district heating circuit and/or into a coal-bearing coal line and/or a fresh air line.
 32. The method as claimed in claim 6, wherein the thermal energy which is decoupled or extracted in the region of the flue gas line and/or in the region of the bypass flue gas line is fed back into a heat exchanger of a reboiler.
 33. The method as claimed in claim 8, wherein the thermal energy is fed back into the reboiler.
 34. The method as claimed in claim 33, wherein the thermal energy is fed back into a heat exchanger of the reboiler.
 35. The power plant of claim 11, wherein the power plant is fossil-fired.
 36. The power plant of claim 11, wherein the power plant is coal-fired.
 37. The power plant of claim 11, wherein a plurality of third plant components that are heat-energy-conductingly connected to said plant component and re also utilized as a heat sink and effect the feeding back into of the decoupled or extracted thermal energy the heat stream of the power plant outside the respective decoupling or extraction region re arranged and/or formed in the region of the power plant.
 38. The power plant as recited in claim 13, wherein the at least one first plant component comprises a heat exchanger.
 39. The power plant as recited in claim 13, wherein the at least one first plant component is for a separate heat-carrier medium.
 40. The power plant as recited in claim 13, wherein the at least one first plant component is formed and is connected in the manner heat-energy-conductingly bearing a separate heat-carrier medium.
 41. The power plant as recited in claim 13, wherein the at least one further plant component comprises a further heat exchanger.
 42. The power plant as recited in claim 13, wherein the at least one further plant component forms a heat sink for the separate heat-carrier medium.
 43. The power plant as recited in claim 14, wherein the heat exchanger forming a heat source at the CO₂ scrubbing station desorber or regenerator head is heat-energy-conductingly connected, to the heat exchanger next to a condensate pump positioned on the upstream side to the condensate flow direction.
 44. The power plant as recited in claim 15, wherein the heat exchanger forming a heat source is heat-energy-conductingly connected downstream of the CO₂ compression to the heat exchanger next to a feed water container in the condensate flow direction, and/or with the heat exchanger, forming a heat sink, upstream of the low-pressure preheater.
 45. The power plant as recited in claim 28, wherein the heat exchanger heat-conductingly connected to the district heating circuit and/or a heat exchanger heat-conductingly connected to the water-steam circuit of the power plant, is in the region of the low-pressure preheater. 